Cody Shale
The Cody Shale is a Late Cretaceous geologic formation. It is mapped in Wyoming, Idaho, and Montana.
| Cody Shale Stratigraphic range: Late Cretaceous | |
|---|---|
| Type | Sedimentary |
| Sub-units | see text |
| Underlies | Mesaverde Formation |
| Overlies | Frontier Formation |
| Thickness | 500-1000 m |
| Lithology | |
| Primary | shale |
| Location | |
| Region | Montana folded belt province, Central Montana uplift, Big Horn basin, Powder River basin, Wind River basin |
| Country | United States |
| Extent | Wyoming, Idaho, Montana |
| Type section | |
| Named for | Cody, Wyoming |
| Named by | C. T. Lupton, 1916[1] |
The formation is described by W.G. Pierce as follows: upper part is buff, sandy shale and thinly laminated buff sandstone; lower part is dark gray, thin-bedded marine shale.[2]
The formation is divided into many members that vary regionally. Alphabetically:[3]
- Ardmore Bentonite Beds (WY)
- Belle Fourche Member (MT, WY)
- Carlile Member (MT, WY)
- Claggett Member (MT, WY)
- Eldridge Creek Member (MT)
- Gammon Ferruginous Member (MT, WY)
- Greenhorn Calcareous Member (MT)
- Niobrara Member (MT, WY)
- Sage Breaks Member (WY)
- Shannon Sandstone Member (MT, WY)
- Steele Member (WY)
- Sussex Sandstone Member (WY)
- Telegraph Creek Member (MT, WY)
- Wallace Creek Tongue (WY)
Certain members rise to formation rank in other areas; for example, the Greenhorn is classified as a formation in a number of states, particularly in Colorado and Kansas.
References
- Lupton, C.T., 1916, Oil and gas near Basin, Big Horn County, Wyoming, IN Contributions to economic geology, 1915; Part 2, Mineral fuels: U.S. Geological Survey Bulletin, 621-L, p. L157-L190.
- Pierce, W.G., 1997, Geologic map of the Cody 1 degree x 2 degrees quadrangle, northwestern Wyoming: U.S. Geological Survey, Miscellaneous Geologic Investigations Map I-2500, scale 1:250000.
- "Geologic Unit: Cody". National Geologic Database. Geolex — Unit Summary. United States Geological Survey. Retrieved 2018-06-29.
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